"Federal Information Processing Standards Publication (FIPS PUB) 46", published on Jan. 15, 1977 defines a Data Encryption Standard (DES) which may be used for encryption and decryption in a plurality of operational modes. Generally, each of the various modes of operation are accomplished by implementation in a circuit designed and fabricated for the particular mode desired in a particular application. This has meant that a supplier to the industry, in order to be responsive to the needs of a variety of DES users, has had to develope and/or inventory circuits of a number of various types in order to serve his customers. As an alternative, he may have to implement some or all of the various modes in a computer. This prior approach to the problem uses computer memory capacity, requires software and results in slower system operation as well as being more expensive in terms of hardware cost and slower operation.